Different embodiments of a cable drum are used industrially for supplying movable or mobile systems with electrical energy. For this purpose, the cable drum is typically assigned to the movable or mobile system and includes an electric line which can be rolled up or unrolled, and of which the free end is connected to a stationary power-supply unit. The rolling-up and unrolling movement is controlled, for example, by means of an electromotive drum drive or winder drive, in accordance with the length of line which is required in each case. In the simplest scenario, instead of an electromotive drum drive or winder drive, use is made of a spring mechanism which pre-stresses the cable drum, and therefore the electric line, during the unwinding operation, and therefore said line is rolled up automatically as the tensile stressing eases off.
Such arrangements are known, for example, in heavy-duty cranes for supplying electricity to a crane truck which is guided in a movable manner along associated rails. Since the movement of the crane truck is securely predetermined, a defined rolling-up and unrolling movement of the electric line is ensured here. In contrast, the conditions in the case of mobile machinery, for example, of an electrically operated agricultural tractor are considerably more complex since the mobile machinery can move freely and, to this extent, it is not possible to rule out a situation where the path over which the vehicle travels crosses in an undesirable manner the unwound line portion lying on the ground. If the vehicle travels over the electric line, this can result in the latter being damaged or even destroyed.
In this disclosure, an arrangement is provided which makes it possible to define the progression, and therefore the position, of a line portion unwound from a cable drum.